1. Field of the Invention
This invention relates to a process for preparing etherified polyoxyalkylene derivatives and, more particularly, relates to an improved process for preparing an etherified polyoxyalkylene derivative by etherifying a polyoxyalkylene compound having at least 4 oxyalkylene units and either one or two terminal hydroxyl groups through use of an organic primary halide and an aqueous solution of alkali metal hydroxide.
2. Description of the Prior Art
Etherification of a polyoxyalkylene compound having at least one terminal hydroxyl group has to date generally been effected by first reacting the polyoxyalkylene compound with an alkali metal or its hydride or alcoholate, such as sodium metal, potassium metal, sodium hydride or sodium hydride or sodium methylate, and then reacting the resultant alcoholate with an organic halide. This method enables the production of various etherified polyoxyalkylene derivatives. Concomitantly, however, the expensive alkali metal or its hydride or alcoholate is consumed stoichiometrically, and the yield of the desired product is at most 60%.
It is also known to prepare ethers of polyoxyalkylene glycol by reacting polyoxyalkylene glycol with an organic halide in the presence of a finely powdered alkali metal hydroxide at an elevated temperature, but this method cannot be conducted continuously and usually requires a higher temperature exceeding 100.degree. C. to facilitate the reaction.
As a rather esoteric case, it is also known that polyoxyalkylene glycol diallyl ether can be produced by reacting polyoxyalkylene glycol with an allyl halide (per se well known as a highly reactive organic halide), even in the presence of an aqueous solution of alkali metal hydroxide. In this particular synthesis, a portion of the allyl halide is hydrolyzed and the yield of diallyl ether of polyoxyalkylene glycol is markedly low.
With regard to etherification by use of an aqueous solution of alkali metal hydroxide, it too is known to produce a polyoxyalkylene glycol dialkyl ether by reacting an aliphatic alcohol or mono-, di- or tri-oxyalkylene glycol monoalkyl ether with a .beta.,.beta.'-dihalogenodialkyl ether in the presence of an aqueous solution having a greater than 20 wt. % concentration of alkali metal hydroxide (German Pat. No. 1,129,147; British Pat. Specification No. 967,585). According to the specifications of the noted German and British patents, although the subject method affords the desired product, i.e., hexa- or octa-alkylene glycol diether, the yield is fairly low (about 58%), and a byproduct, i.e., tetra- or penta-alkylene glycol alkyl vinyl ether is formed in an about 30-40% yield. Since the polyoxyalkylene glycol diethers have a higher boiling point, it is virtually impossible to separate the desired product exclusively from the reaction mixture containing the desired product and high boiling byproducts.
In addition to the methods described above, the following methods for the etherification of polyoxyalkylene compounds having at least one terminal hydroxyl group are known: (i) a method comprising replacing the terminal hydroxyl group of the said polyoxyalkylene compound with a chlorine atom by reaction with thionyl chloride, followed by further reaction of the resultant chlorinated polyoxyalkylene compound with a metal alkoxide; (ii) a method comprising converting the terminal hydroxyl group of the said polyoxyalkylene compound into tosylate by reaction with a tosyl halide, i.e., p-toluene sulfohalide, and then further reacting the tosylate with an alkyl halide; (iii) a method of etherification with dialkyl sulfate; and (iv) a method of methyl etherification with formaldehyde. The methods (i) and (ii) are disadvantageous in view of requirement of two-stage reactions. Moreover, the raw materials used in these methods, i.e., thionyl chloride, metal alkoxide and tosyl halide, are too expensive from the viewpoint of their quantitative consumption. Dialkyl sulfate used in the method (iii) is also expensive and, for practical purposes, this synthesis is limited only to dimethyl sulfate which is extremely harmful to human health. The method (iv) is applicable only to methyl etherification.